A typical hydraulic lash adjuster (HLA) comprises a first oil chamber defined between an outer body and a plunger assembly slidably mounted within the outer body, and a spring biased to enlarge the first oil chamber by pushing the plunger assembly outwardly from the outer body to extend the HLA. Typically, the HLA has a second oil chamber, defined by the plunger assembly and which is in fluid communication with the engine's oil supply. The first oil chamber and the second oil chamber are separated by a one way valve and oil flows from the second chamber into the first chamber through the one way valve when the HLA extends (and hence the first chamber enlarges) because the oil pressure in the second chamber becomes higher than that in the first chamber. Whereas oil can flow into the first pressure chamber via the one way valve, it can only escape the first pressure chamber very slowly, for example, via closely spaced leak down surfaces. Accordingly, a HLA can extend to accommodate any slack in a valve train assembly, such as between the cam and the roller but after it is extended, the incompressible oil in the first chamber provides sufficient rigid support for the HLA to open the valve when a rocker arm pivots (i.e. the incompressible oil prevents the plunger assembly being pushed back inwardly of the outer body so that the HLA acts as a solid body).
Compression engine brakes are typically used as auxiliary brakes, in addition to wheel brakes, on relatively large vehicles, for example trucks, powered by heavy or medium duty diesel engines. A compression engine braking system is arranged, when activated, to provide an additional opening of an engine cylinder's exhaust valve when the piston in that cylinder is close to the top-dead-center position of its compression stroke so that compressed air is released through the exhaust valve. This causes the engine to function as a power consuming air compressor which slows the vehicle.
In a typical valve train assembly used with a compression engine brake, the exhaust valve is actuated by a rocker arm to provide an additional compression brake exhaust valve lift in addition to the main exhaust valve lift. The rocker arm rocks in response to a cam on a rotating cam shaft and acts on the exhaust valve, either directly, or indirectly (for example, by means of a valve bridge) to open it. Lost motion variable valve actuation systems may be used to inhibit the additional compression brake exhaust valve lift when the engine is in normal engine combustion mode.
A hydraulic lash adjuster may also be provided in the valve train assembly to remove any lash (i.e. gap) that develops between components in the valve train assembly.
U.S. Pat. No. 7,156,062 describes a valve actuation system that comprises a lost motion system and a separate, distinct automatic lash adjuster. The system is complicated and has a large number of distinct components.
U.S. Pat. No. 7,484,483 describes a variable valve actuation system that comprises a manual lash adjuster. Manual lash adjusters have the disadvantage of not providing automatic lash adjustment. Instead, a mechanic must adjust a manual lash adjuster during engine servicing.